Turbine engine and method of operating

ABSTRACT

A method of operating a turbine engine that includes actuating a starter motor of the turbine engine such that a motoring speed of the turbine engine increases, and actuating a plurality of variable stator vanes of the turbine engine such that the plurality of variable stator vanes are at least partially open to control the motoring speed of the turbine engine.

BACKGROUND

The present disclosure relates generally to turbine engines and, morespecifically, to systems and methods of mitigating thermal rotor bow inturbine engines.

Turbine engines, such as turbofan engines, experience several differentphases of operation including, but not limited to, startup to idlespeed, warmup, acceleration to higher power and speed for takeoff,climb, cruise, steady-state, deceleration to lower speed and power fordescent, landing and taxi, shutdown, and cool-down. Turbine engines maycycle through the different phases of operation several times a daydepending on the use of the aircraft to which the turbine engines areattached. For example, a commercial passenger aircraft typically shutsdown its engines in between flights as passengers disembark from theaircraft. As such, residual heat remains in the aircraft's engines,which can cause a phenomenon known as thermal rotor bow. Thermal rotorbow is generally defined by deformation in the rotating and stationarycomponents of the turbine engine. Deformation in the components of theturbine engine can result in contact-related damage between the rotatingand stationary components of the turbine engine during engine startup,thereby reducing the service life, performance, and operability of theturbine engine.

Thermal rotor bow is especially prominent at times after engineshutdown, and before the engine is allowed to fully cool. Moreover, manyknown turbine engines are unable to naturally mitigate thermal rotor bowduring startup as the design of modern commercial turbofans shiftstowards having higher bypass ratios and greater length-to-diameterratios, as well as tighter clearances between rotors and stators of theengine.

BRIEF DESCRIPTION

In one aspect, a method of operating a turbine engine is provided. Themethod includes actuating a starter motor of the turbine engine suchthat a motoring speed of the turbine engine increases, and actuating aplurality of variable stator vanes of the turbine engine such that theplurality of variable stator vanes are at least partially open tocontrol the motoring speed of the turbine engine.

In another aspect, a turbine engine is provided. The turbine engineincludes a starter motor, a compressor assembly including a plurality ofvariable stator vanes, and a computing device coupled in communicationwith the starter motor and the plurality of variable stator vanes. Thecomputing device is configured to actuate the starter motor of theturbine engine such that a motoring speed of the turbine engineincreases, and actuate the plurality of variable stator vanes such thatthe plurality of variable stator vanes are at least partially open tocontrol the motoring speed of the turbine engine.

In yet another aspect, a computer-readable medium havingcomputer-executable instructions embodied thereon for use in operating aturbine engine is provided. When executed by at least one processor, thecomputer-executable instructions cause the processor to actuate astarter motor of the turbine engine such that a motoring speed of theturbine engine increases, and actuate a plurality of variable statorvanes of the turbine engine such that the plurality of variable statorvanes are at least partially open to control the motoring speed of theturbine engine.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic illustration of an exemplary turbine engine;

FIG. 2 is a schematic illustration of an exemplary starter system thatmay be used to actuate the turbine engine shown in FIG. 1;

FIG. 3 is a radial illustration of a portion of a compressor assemblythat may be used in the turbine engine shown in FIG. 1, wherein thecompressor assembly is in a first operational position;

FIG. 4 is a radial illustration of the portion of the compressorassembly shown in FIG. 3 in a second operational position;

FIG. 5 is a logic diagram illustrating an exemplary method of operatingthe turbine engine shown in FIG. 1;

FIG. 6 is a logic diagram illustrating an exemplary method ofdetermining a startup procedure to execute;

FIG. 7 is a logic diagram illustrating an exemplary method of manuallystarting the turbine engine shown in FIG. 1; and

FIG. 8 is a logic diagram illustrating an alternative method of manuallystarting the turbine engine shown in FIG. 1.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of the disclosure. These features arebelieved to be applicable in a wide variety of systems including one ormore embodiments of the disclosure. As such, the drawings are not meantto include all conventional features known by those of ordinary skill inthe art to be required for the practice of the embodiments disclosedherein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made toa number of terms, which shall be defined to have the followingmeanings.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, “approximately”, and “substantially”, are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged. Such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

As used herein, the terms “axial” and “axially” refer to directions andorientations that extend substantially parallel to a centerline of theturbine engine. Moreover, the terms “radial” and “radially” refer todirections and orientations that extend substantially perpendicular tothe centerline of the turbine engine. In addition, as used herein, theterms “circumferential” and “circumferentially” refer to directions andorientations that extend arcuately about the centerline of the turbineengine.

As used herein, the terms “processor” and “computer,” and related terms,e.g., “processing device,” “computing device,” and “controller” are notlimited to just those integrated circuits referred to in the art as acomputer, but broadly refers to a microcontroller, a microcomputer, aprogrammable logic controller (PLC), and application specific integratedcircuit, and other programmable circuits, and these terms are usedinterchangeably herein. In the embodiments described herein, memory mayinclude, but it not limited to, a computer-readable medium, such as arandom access memory (RAM), a computer-readable non-volatile medium,such as a flash memory. Alternatively, a floppy disk, a compactdisc-read only memory (CD-ROM), a magneto-optical disk (MOD), and/or adigital versatile disc (DVD) may also be used. Also, in the embodimentsdescribed herein, additional input channels may be, but are not limitedto, computer peripherals associated with an operator interface such as amouse and a keyboard. Alternatively, other computer peripherals may alsobe used that include, for example, but not be limited to, a scanner.Furthermore, in the exemplary embodiment, additional output channels mayinclude, but not be limited to, an operator interface monitor.

Further, as used herein, the terms “software” and “firmware” areinterchangeable, and include any computer program storage in memory forexecution by personal computers, workstations, clients, and servers.

As used herein, the term “non-transitory computer-readable media” isintended to be representative of any tangible computer-based deviceimplemented in any method of technology for short-term and long-termstorage of information, such as, computer-readable instructions, datastructures, program modules and sub-modules, or other data in anydevice. Therefore, the methods described herein may be encoded asexecutable instructions embodied in a tangible, non-transitory,computer-readable medium, including, without limitation, a storagedevice and/or a memory device. Such instructions, when executed by aprocessor, cause the processor to perform at least a portion of themethods described herein. Moreover, as used herein, the term“non-transitory computer-readable media” includes all tangible,computer-readable media, including, without limitation, non-transitorycomputer storage devices, including without limitation, volatile andnon-volatile media, and removable and non-removable media such asfirmware, physical and virtual storage, CD-ROMS, DVDs, and any otherdigital source such as a network or the Internet, as well as yet to bedeveloped digital means, with the sole exception being transitory,propagating signal.

Embodiments of the present disclosure relate to systems and methods foruse in mitigating thermal rotor bow in a turbine engine. Morespecifically, in one embodiment, feedback on one or more operatingparameters of the turbine engine is used to determine a motoring timefor the turbine engine that will result in sufficient thermal rotor bowmitigation for engine startup. For example, in one embodiment, themotoring time is selected from multiple preset motoring times that eachcorrespond to a different value of the one or more operating parameters.The one or more parameters are monitored as the rotor assembly of theturbine engine is rotated for the selected motoring time, and feedbackis further used to dynamically adjust the motoring time if adetermination is made to implement additional or less rotor bowmitigation. As such, thermal rotor bow is mitigated in a timely andefficient manner.

In another embodiment, the systems and methods described hereinfacilitate controlling the rotational speed of the turbine engine duringstartup motoring thereof. The rotational speed of the turbine engine iscontrolled by selectively actuating variable stator vanes includedwithin the turbine engine, by controlling the power output of a startersystem coupled to the turbine engine, and by a combination thereof.Actuating the variable stator vanes into an at least partially openposition during engine startup increases counter-rotational torque onthe rotor assembly of the turbine engine, which facilitates reducing therotational speed of the turbine engine. In one embodiment, the poweroutput of the starter system is controlled with a series of valves thatcontrol airflow in the starter system, such as a modulating valve in anauxiliary power unit (APU) and a starter valve coupled between the APUand a starter motor. The valves facilitate adjusting the power output ofthe starter motor, and controlling multiple control valves enablesdifferent levels of adjustment of the power output to be provided. Assuch, the rotational speed of the turbine engine is controlled in aprecise manner for reduction of the rotational speed to less than aresonant rotational speed, which may result in unwanted vibration andpotential contact between rotating and stationary components in theturbine engine. Alternatively, controlling the rotational speed of theturbine engine enables incremental increases in the rotational speed ofthe turbine engine to be made as thermal rotor bow is progressivelymitigated. As such, the motoring time of the turbine engine is reduced.

As used herein, “resonant rotational speed” refers to a singlerotational speed or a range of rotational speeds of the turbine enginethat causes high dynamic vibration or displacement in the presence of arotor imbalance such as thermal rotor bow.

In many modern turbine engines, the control valve that controls airflowto the starter motor is also referred to as a starter air valve. Thestarter air valve is typically actuated by full authority digital enginecontrol (FADEC) motoring logic that selectively actuates the starter airvalve, and that determines if the starter air valve is in a closedposition or an open position. In the event of a malfunction in theactuation of the starter air valve by the FADEC motoring logic, thestarter air valve is accessible to ground personnel to facilitate manualactuation of the starter air valve and manual startup of the turbineengine. A power output of the starter motor can sometimes be modulatedwith additional FADEC motoring logic that selectively actuates thestarter air valve into intermediate positions between the closedposition and the open position. However, known FADEC motoring logic maygenerate a fault when the starter air valve is manually actuated into anopen position, thereby preventing startup of the turbine engine.

Accordingly, another embodiment of the present disclosure relates tosystems and methods for use in manually starting a turbine engine bybypassing normal FADEC pre-lightoff motoring logic. More specifically,the systems and methods described herein include a FADEC system having aprimary startup procedure and a secondary startup procedure. The primarystartup procedure includes logic for automatically adjusting a poweroutput of a starter motor of the turbine engine. More specifically, theprimary startup procedure includes logic for selectively actuating astarter air valve from a closed position into a fully open position, oran intermediate position defined therebetween based on a desiredmotoring speed of the turbine engine. In the event of a malfunction inautomatically adjusting the power output of the starter motor, a faultis generated in the system and the primary startup procedure is unableto be executed. In such a scenario, during a subsequent start attempt,the FADEC system bypasses the primary startup procedure and executes asecondary startup procedure that does not include logic for selectivelyactuating the starter air valve. As such, the FADEC system includeslogic that enables manual startup of the turbine engine, and that iscompliant with parallel logic that automatically adjusts the motoringspeed of the turbine engine.

While described in the context of a turbofan engine, it should beunderstood that the systems and methods described herein are alsoapplicable to turboprop engines, turboshaft engines, turbojet engines,and any other turbine engine where thermal rotor bow mitigation isdesired. Moreover, as will be described in more detail below, any of theembodiments described herein may be used, either alone or incombination, to facilitate controlling startup of a turbine engine.

FIG. 1 is a schematic illustration of an exemplary turbine engine 10,such as a turbofan engine. Turbine engine 10 includes a fan assembly 12,a low-pressure or booster compressor assembly 14, a high-pressurecompressor assembly 16, and a combustor assembly 18. Fan assembly 12,booster compressor assembly 14, high-pressure compressor assembly 16,and combustor assembly 18 are coupled in flow communication. Turbineengine 10 also includes a high-pressure turbine 20 coupled in flowcommunication with combustor assembly 18 and a low-pressure turbine 22.Fan assembly 12 includes an array of fan blades 24 extending radiallyoutward from a rotor disk 26. Low-pressure turbine 22 is coupled to fanassembly 12 and booster compressor assembly 14 through a first driveshaft 28, and high-pressure turbine 20 is coupled to high-pressurecompressor assembly 16 through a second drive shaft 30. Turbine engine10 has an intake 32 and an exhaust 34. Turbine engine 10 furtherincludes a centerline 36 about which fan assembly 12, booster compressorassembly 14, high-pressure compressor assembly 16, and turbines 20 and22 rotate.

Turbine engine 10 may also include a starter motor 38 and a startershaft 40 coupled to the rotor assembly of turbine engine 10. Morespecifically, in one embodiment, starter shaft 40 is coupled to seconddrive shaft 30, and starter motor 38 provides motoring power to turbineengine 10 during startup thereof via starter shaft 40. In someembodiments, and as will be explained in further detail below, startermotor 38 is actuated by any suitable source of pneumatic airflow, suchas an APU, another engine, or a static pressure tank. Alternatively,starter motor 38 is actuated by a power source other than pneumaticairflow, such as electricity.

In operation, a portion of air entering turbine engine 10 through intake32 is channeled through fan assembly 12 towards booster compressorassembly 14. Compressed air is discharged from booster compressorassembly 14 towards high-pressure compressor assembly 16. Highlycompressed air is channeled from high-pressure compressor assembly 16towards combustor assembly 18, mixed with fuel, and the mixture iscombusted within combustor assembly 18. High temperature combustion gasgenerated by combustor assembly 18 is channeled towards turbines 20 and22. Combustion gas is subsequently discharged from turbine engine 10 viaexhaust 34.

FIG. 2 is a schematic illustration of an exemplary starter system 42that may be used to actuate turbine engine 10. In the exemplaryembodiment, starter system 42 includes starter motor 38 and an auxiliarypower unit (APU) 44 coupled in a serial flow relationship. Morespecifically, APU 44 channels airflow towards starter motor 38 along ableed line 46, and starter motor 38 converts the energy of the airflowto a mechanical output to facilitate actuating turbine engine 10. Acontrol valve, such as a starter air valve (SAV) 50, is coupled alongbleed line 46 to control airflow channeled from APU 44 towards startermotor 38. SAV 50 is either a two-position valve (i.e., a valvepositionable between an open position and a closed position) or amulti-position valve (i.e., a valve positionable in a closed position,an open position, and at intermediate positions between the closedposition and the open position). As such, in one embodiment, SAV 50 isselectively positioned in the open position, the closed position, or oneof the intermediate positions to control the airflow channeled towardsstarter motor 38. Moreover, the position of SAV 50 may be dynamicallyadjusted during operation of starter motor 38 to control the motoringspeed of turbine engine 10, as will be explained in more detail below.

In an alternative embodiment, starter motor 38 receives airflow from apneumatic power source other than APU 44 such as, but not limited to, analready-started turbine engine or a static pressure tank located onboarda ground cart, for example. In addition, starter motor 38 may beactuated by a power source other than pneumatic airflow, such aselectricity.

Starter system 42 further includes a computing device for controllingstartup of turbine engine 10. In the exemplary embodiment, the computingdevice is onboard turbine engine 10, such as a full authority digitalengine control (FADEC) system 52. FADEC system 52 is coupled, either bywired or wirelessly connectivity, in communication with one or moresubsystems or components of turbine engine 10 and starter system 42 tocontrol the operation of turbine engine 10 and starter system 42 atvarious stages of operation of turbine engine 10. For example, FADECsystem 52 is coupled in communication with starter motor 38 and APU 44for controlling the motoring time and the motoring speed of turbineengine 10. More specifically, FADEC system 52 is coupled incommunication with SAV 50, a modulating valve 54 of APU 44, and variablestator vanes 56 of turbine engine 10 for controlling the motoring timeand the motoring speed of turbine engine 10, as will be explained inmore detail below. In an alternative embodiment, the subsystems orcomponents of turbine engine 10 and starter system 42 are controlled bya computing device onboard an aircraft (not shown) in which turbineengine 10 is attached.

One or more feedback sensors 58 are also coupled in communication withFADEC system 52. Feedback sensors 58 and FADEC system 52 monitor one ormore operating parameters of turbine engine 10. Depending on theoperating parameters monitored, feedback sensors 58 also transmitfeedback to FADEC system 52 for use in determining at least one of amotoring time or a motoring speed for turbine engine 10 that will resultin thermal rotor bow mitigation. In an alternative embodiment, FADECsystem 52 uses feedback from feedback sensors 58 to facilitate operatingturbine engine 10 at a motoring speed less than a resonant rotationalspeed when mitigating thermal rotor bow, as will be described in moredetail below. Example operating parameters of turbine engine 10 include,but are not limited to, a temperature within turbine engine 10, anambient temperature outside turbine engine 10, a vibratory response ofturbine engine 10 when rotated at a motoring speed, a dynamic or staticclearance between rotating and stationary components of turbine engine10, a rotational or motoring speed of turbine engine 10, and an amountof time since shutdown of turbine engine 10.

In operation, FADEC system 52 monitors at least one operating parameterof turbine engine 10, and determines a preset motoring time for turbineengine 10 based on a value of the at least one operating parameter.Determining how long to motor turbine engine 10 is balanced inconsideration of how long it takes to mitigate thermal rotor bow and thedesire to startup turbine engine 10 in a timely fashion. Moreover, morethan one operating parameter may be used by FADEC system 52 to moreaccurately determine the preset motoring time. More than one operatingparameter may also be monitored by FADEC system 52 such that FADECsystem 52 is capable of determining a motoring time for turbine engine10 in the event one or more feedback sensors 58 become inoperable, or inthe event of another technical malfunction related to monitoring theoperating parameters of turbine engine 10. Moreover, in someembodiments, the determined preset motoring time is zero based on thevalue of the at least one operating parameter.

For example, in one embodiment, FADEC system 52 determines the presetmotoring time based on one or more temperature readings determined atthe beginning of an engine startup cycle. Comparatively low temperatureswithin turbine engine 10 may indicate that turbine engine 10 has beenshut down for a long period of time such that thermal rotor bow has beennaturally mitigated. Low temperatures may also indicate that turbineengine 10 was previously turned on at a low power setting such thatformation of thermal rotor bow is less severe. In contrast,comparatively high temperatures within turbine engine 10 may indicatethat turbine engine 10 has been shut down for a period of time resultingin more severe formation of thermal rotor bow. As such, in someembodiments, the determined preset motoring time is shorter when thetemperature within turbine engine 10 is comparatively low, and thedetermined preset motoring time is longer when the temperature withinturbine engine 10 is comparatively high. In an alternative embodiment,FADEC system 52 determines the preset motoring time based on the amountof time since shutdown of turbine engine 10.

In addition to monitoring the temperature within turbine engine 10, inone embodiment, FADEC system 52 also monitors a temperature of anambient environment outside turbine engine 10. FADEC system 52determines a temperature difference (i.e., a thermal gradient) betweenthe temperature within turbine engine 10 and the temperature of theambient environment, and determines the preset motoring time based on avalue of the temperature difference. A determination of the magnitude ofa thermal gradient across turbine engine 10 provides a potentially morerobust and accurate determination of the severity of thermal rotor bowformation.

In one embodiment, the preset motoring time is selected from a pluralityof preset motoring times stored within FADEC system 52. For example, thepreset motoring times may be in a format such as, but not limited to, aninterpolated lookup table. The plurality of preset motoring times arepredetermined based on the characteristics of the turbine enginecontrolled by FADEC system 52. Each preset motoring time of theplurality of preset motoring times corresponds to a different value ofthe at least one operating parameter. In addition, when the presetmotoring time is determined based on multiple operating parameters, thevalue of each operating parameter may be given equal weight or weighteddifferently when determining the preset motoring time. In an alternativeembodiment, FADEC system 52 calculates the preset motoring time at eachstartup cycle using an algorithm stored therein.

Once the preset motoring time is determined, FADEC system 52 actuatesstarter motor 38 such that turbine engine 10 is rotated at a motoringspeed. In one embodiment, starter motor 38 is actuated for at least thepreset motoring time. FADEC system 52 also continues to monitor one ormore operating parameters of turbine engine 10 to determine whether todynamically adjust the motoring time of turbine engine 10 after thepreset motoring time has expired. For example, in the exemplaryembodiment, FADEC system 52 and feedback sensors 58 monitor a vibratoryresponse of turbine engine 10 as turbine engine 10 is rotated at themotoring speed for the preset motoring time, and FADEC system 52 addsadditional time to the preset motoring time based on the value of thevibratory response. The value or severity of the vibratory response isgenerally indicative of the continued existence of thermal rotor bowwhen motoring turbine engine 10. For example, turbine engine 10experiences a greater vibratory response at motoring speeds at or nearthe resonant rotational speed of turbine engine 10. As such, in theevent actuation of starter motor 38 for the preset motoring time hasinsufficiently mitigated thermal rotor bow, FADEC system 52 increasesthe motoring time of turbine engine 10. In one embodiment, FADEC system52 increases the motoring time when the value of the vibratory responseis greater than a predetermined threshold at the conclusion of thepreset motoring time. Alternatively, the motoring time of turbine engine10 is reduced based on the vibratory response. Operating parametersother than vibratory response, as described above, may be monitored todetermine whether to dynamically adjust the motoring time of turbineengine 10.

When the motoring time of turbine engine 10 is increased, FADEC system52 also includes logic for shutting down starter motor 38 after startermotor 38 operates for a preset time, and firing turbine engine 10 evenif the preset time has been reached. More specifically, the preset timeis determined as a function of a theoretical maximum time to beimplemented for mitigating a theoretical thermal rotor bow. Thetheoretical maximum time is based on a worst-case estimate of themagnitude of thermal rotor bow. If the theoretical maximum time has beenreached and the vibratory response, for example, is still greater thanthe predetermined threshold, a malfunction may have occurred and turbineengine 10 is started. As such, the motoring time of turbine engine 10can only be increased up to the preset time, which reduces unnecessarywear to starter motor 38.

As described above, motoring turbine engine 10 progressively decreasesthe severity of thermal rotor bow as a function of time. In general,thermal rotor bow is more rapidly mitigated at higher motoring speed. Inone embodiment, lessening the severity of thermal rotor bow enablesincremental increases to the motoring speed of turbine engine 10 to bemade, such that overall motoring time of turbine engine 10 is reduced.As such, FADEC system 52 also monitors the vibratory response of turbineengine 10 to determine when the motoring speed of turbine engine 10 canbe modified. More specifically, FADEC system 52 monitors turbine engine10 for an adjustment in the value of the vibratory response as turbineengine 10 is rotated at the motoring speed, and increases the motoringspeed of turbine engine 10 when the vibratory response decreases.

FADEC system 52 modifies the motoring speed of turbine engine 10 usingone or more control arrangements, utilized separately or in combinationwith each other. For example, FADEC system 52 selectively actuates atleast one valve in starter system 42 and/or variable stator vanes 56 inturbine engine 10 to control the motoring speed of turbine engine 10. Insome embodiments, the control arrangements increase the motoring speedof turbine engine 10 to reduce motoring time or, in the alternative,reduce the motoring speed of turbine engine 10 to facilitate motoringturbine engine 10 at a motoring speed less than the resonant rotationalspeed.

In one embodiment, referring to FIG. 2, FADEC system 52 is coupled incommunication with SAV 50 and modulating valve 54 for controllingactuation thereof. Controlling actuation of SAV 50 and modulating valve54 enables the motoring speed of turbine engine 10 to be controlled in amore precise and responsive manner, with redundancy, when compared to asingle valve actuation control arrangement. For example, controllingmotoring speed of turbine engine 10 with only modulating valve 54 mayresult in communication latency and physical lag due to an increasedflowpath distance between modulating valve 54 and starter motor 38, whencompared to the flowpath distance between SAV 50 and starter motor 38.

In operation, FADEC system 52 actuates and holds modulating valve 54 ata predetermined position such that APU 44 provides a predetermined poweroutput to starter motor 38. The predetermined power output is selectedsuch that, if SAV 50 were in a fully open position, the motoring speedof turbine engine 10 would be slightly greater than the resonantrotational speed. As such, FADEC system 52 adjusts a position of SAV 50to control the motoring speed of turbine engine 10. More specifically,FADEC system 52 actuates SAV 50 into an at least partially closedposition to reduce the motoring speed of turbine engine 10 below theresonant rotational speed. FADEC system 52 also dynamically adjusts theposition of SAV 50 based on the vibratory response of turbine engine 10,for example, to increase or decrease the motoring speed of turbineengine 10.

In an alternative embodiment, the amount of power provided to startermotor 38 from APU 44 is adjusted to control the motoring speed ofturbine engine 10. In one embodiment, as described above, the positionof modulating valve 54 is adjusted to control the motoring speed. Inaddition or in the alternative, the position of inlet guide vanes orcompressor stator vanes within APU 44 may be adjusted, the position ofan output modulating valve positioned between APU 44 and starter motor38 may be adjusted, an accessory load may be pulled from APU 44, and/orfuel flow provided to APU 44 may be adjusted to control the motoringspeed.

Moreover, in one embodiment, the motoring speed of turbine engine 10 iscontrolled by actuating valves other than, or in addition to, SAV 50 andmodulating valve 54. The additional valves other than SAV 50 andmodulating valve 54 control airflow channeled towards starter motor 38when a source of pneumatic power other than APU 44 is used to actuatestarter motor 38. For example, starter motor 38 may be actuated by apower source other than APU 44. In such an embodiment, when feasible,FADEC system 52 controls a power output of the power source such thatthe predetermined power output is provided to starter motor 38. Forexample, when cross-bleeding from an already-started turbine engine 57,FADEC system 52 may control actuation of a bleed valve 59 withinalready-started turbine engine 57, or a control valve 61 coupled along ableed line 63 extending between already-started turbine engine 57 andstarter motor 38, to control the motoring speed of turbine engine 10. Afurther additional valve for controlling the motoring speed of turbineengine 10 includes discharge or bypass valve 55, which is selectivelyactuatable to reduce an amount of airflow channeled into starter motor38.

Actuation of SAV 50, modulating valve 54, additional valves describedabove, or a combination thereof, may be used additionally with actuationof variable stator vanes 56 to increase or decrease the motoring speedof turbine engine 10. Alternatively, when starter motor 38 is actuatedby electricity, FADEC system 52 controls the power output of theelectric motor to control the motoring speed of turbine engine 10.

FIG. 3 is a radial illustration of a portion of a compressor assembly,such as high-pressure compressor assembly 16, that may be used inturbine engine 10 (shown in FIG. 1), wherein high-pressure compressorassembly 16 is in a first operational position (i.e., a closedposition), and FIG. 4 is a radial illustration of the portion ofhigh-pressure compressor assembly 16 in a second operational position(i.e., an at least partially open position). As described above, FADECcontrol of variable stator vanes 56 is one of many control arrangementsfor controlling the motoring speed of turbine engine 10. In theexemplary embodiment, high-pressure compressor assembly 16 includes atleast one row 60 of a plurality of rotor blades 62, and at least one row64 of a plurality of variable stator vanes 56 positioned downstream fromrow 60. The plurality of rotor blades 62 rotate in a circumferentialdirection 66 relative to centerline 36 (shown in FIG. 1), and theplurality of variable stator vanes 56 remain substantially stationary(i.e., non-rotating in circumferential direction 66) relative to therotation of the plurality of rotor blades 62. In an alternativeembodiment, row 64 is positioned upstream from row 60.

The plurality of variable stator vanes 56 are selectively actuatable,either individually or together, between a closed position and an atleast partially open position. More specifically, the plurality ofvariable stator vanes 56 are rotatable about a radial axis (not shown)that extends radially relative to centerline 36. Opening the pluralityof variable stator vanes 56 increases counter-rotational torque on therotor assembly of turbine engine 10, which reduces the motoring orrotational speed of turbine engine 10. In contrast, closing theplurality of variable stator vanes 56 reduces counter-rotational torqueon the rotor assembly of turbine engine 10, which increases the motoringor rotational speed of turbine engine 10. In some embodiments, theplurality of variable stator vanes 56 are positionable at intermediatepositions between the closed position and a fully open position.Moreover, the closed position of variable stator vanes 56 is generallydefined by the size of a clearance between adjacent variable statorvanes 56 in row 64 (i.e., variable stator vanes 56 are closed when theclearance can no longer be reduced when rotating vanes 56 about theradial axis).

As described above, FADEC system 52 (shown in FIG. 1) is coupled, eitherby wired or wirelessly connectivity, in communication with the pluralityof variable stator vanes 56. More specifically, FADEC system 52 iscapable of selectively and dynamically positioning the plurality ofvariable stator vanes 56 in the closed position, the open position, orvarious intermediate positions in response to fluctuations in themotoring speed of turbine engine 10, or based on a desired motoringspeed of turbine engine 10. In an alternative embodiment, FADEC system52 selectively actuates inlet guide vanes (not shown) of high-pressurecompressor assembly 16, or inlet guide vanes of booster compressorassembly 14 to control the motoring speed of turbine engine 10.

In one embodiment, prior to startup of turbine engine 10, variablestator vanes 56 are in the closed position. During startup, FADEC system52 actuates starter motor 38 (shown in FIG. 1) of turbine engine 10 suchthat a rotational speed of turbine engine 10 is increased. Starter motor38 is sometimes actuated at a power output such that turbine engine 10is potentially rotated at a motoring speed greater than the resonantrotational speed when variable stator vanes 56 are in the closedposition. FADEC system 52 actuates the plurality of variable statorvanes 56 into an at least partially open position to reduce the motoringspeed of turbine engine 10. More specifically, FADEC system 52 adjuststhe position of the plurality of variable stator vanes 56 from theclosed position into an at least partially open position such that themotoring speed of turbine engine 10 is reduced. Alternatively, asdescribed above, other control arrangements, such as single or multiplevalve actuations via FADEC control, can be used alone, or in combinationwith actuation of variable stator vanes 56, to reduce the motoring speedof turbine engine 10.

The motoring speed implemented by FADEC control of variable stator vanes56 is determined as a function of the desire for timely mitigation ofthermal rotor bow and the desire to reduce contact-related wear inturbine engine 10. As such, in one embodiment, the position of variablestator vanes 56 is adjusted such that the motoring speed is greater thana predetermined motoring speed and less than the resonant rotationalspeed. For example, the predetermined motoring speed is determined basedon the resonant rotational speed, and is set to a maximum value relativeto the resonant rotational speed that will not cause unacceptable levelsof vibration and engine component damage in the presence of thermalrotor bow.

As described above, motoring turbine engine 10 decreases the severity ofthermal rotor bow as a function of time, which enables incrementalincreases to the motoring speed of turbine engine 10 to be made. Forexample, the motoring speed may be increased to a maximum value thatwill not cause unacceptable levels of vibration and engine componentdamage in the presence of thermal rotor bow. As such, FADEC system 52adjusts the positions of one or more valves (e.g., valves 50, 54, 55,59, and 61) and/or the position of the plurality of variable statorvanes 56 such that the motoring speed of turbine engine 10 is as closeto the maximum value as possible to increase the cooling efficiency andmitigating effects of motoring turbine engine 10. In one embodiment,FADEC system 52 monitors the vibratory response of turbine engine 10 todetermine how much and when the motoring speed of turbine engine 10 canbe increased. When increasing the motoring speed of turbine engine 10,FADEC system 52 closes variable stator vanes 56 to reducecounter-rotational torque on turbine engine 10. As such, motoring timeof turbine engine 10 is reduced. FADEC system 52 may also monitor otheroperating parameters, as described above, to determine how much and whenthe motoring speed of turbine engine 10 can be increased.

In an alternative embodiment, FADEC system 52 monitors a vibratoryresponse of turbine engine 10, and adjusts the position of the pluralityof variable stator vanes 56 such that the vibratory response is lessthan a predetermined threshold.

FIGS. 5-8 are logic diagrams illustrating exemplary methods of operatingturbine engine 10 (shown in FIG. 1). More specifically, FIGS. 5, 7, and8 illustrate crew logic for starting turbine engine 10, and FIG. 6illustrates FADEC logic for starting turbine engine 10. As describedabove, the formation of thermal rotor bow in first drive shaft 28 andsecond drive shaft 30 (each shown in FIG. 1), for example, can occurafter shutdown of turbine engine 10 and before turbine engine 10 hasfully cooled. The primary startup procedure includes logic formitigating thermal rotor bow prior to engaging combustor assembly 18(shown in FIG. 1), and for adjusting the power output of starter motor38 (shown in FIG. 1). While described in the context of SAV 50, thelogic described herein may also be applied when attempting manual startof turbine engine 10 by manually opening valves 54, 59, and 61 (eachshown in FIG. 2), for example.

Referring to FIGS. 5 and 6, in operation, a cockpit crew attemptsstartup of turbine engine 10 in which FADEC system 52 (shown in FIG. 2)executes the primary startup procedure. As described above, the primarystartup procedure includes an automatic mode of actuation of SAV 50(shown in FIG. 1). In one embodiment, FADEC system 52 determines themode of actuation of SAV 50 (shown at box 100). For example, FADECsystem 52 determines SAV 50 was opened with the automatic mode ofactuation based on whether SAV 50 was opened with FADEC command, and thenon-existence of a malfunction when FADEC system 52 attempts toselectively actuate SAV 50. When SAV 50 is opened with FADEC command,the ground crew does not need to manually open SAV 50 (shown at box 102)and the primary startup procedure is executed (shown at box 104).

If the primary startup procedure fails to start turbine engine 10, suchas when SAV 50 fails to open via FADEC command, a first fault istriggered and the cockpit crew terminates the startup procedure. SAV 50is then manually opened, and the cockpit crew restarts the startupprocedure. Manually opening SAV 50 triggers a second fault in FADECsystem 52, which causes the primary startup procedure to be bypassed.For example, upon receiving the startup command, FADEC system 52determines the mode of actuation of SAV 50 from the closed position tothe at least partially open position, and executes the secondary startupprocedure (shown at box 106) when FADEC control of SAV 50 isnon-functional (shown at box 108) and it is determined that SAV 50 hasbeen opened manually. As such, the primary startup procedure isbypassed, which causes the secondary startup procedure to be executed.In an alternative embodiment, FADEC system 52 receives feedback on thephysical position of SAV 50.

As described above, FADEC system 52 determines SAV 50 was opened withthe manual mode of actuation based on the existence of at least onemalfunction in the automatic mode of actuation. The malfunction isdefined by a failure of the control logic in FADEC system 52 inselectively actuating SAV 50 between the closed position and the atleast partially open position. For example, the malfunction can be atleast one of a mechanical failure at SAV 50, an electrical failure, andcommunications failure between FADEC system 52 and SAV 50. If the modeof actuation is not the automatic mode of actuation (i.e., the mode ofactuation is the manual mode of actuation), FADEC system 52 executes thesecondary startup procedure. The secondary startup procedure does notinclude logic for mitigating thermal rotor bow prior to engagingcombustor assembly 18, and does not include logic for adjusting thepower output of starter motor 38 such that a fault is not generated whenFADEC system 52 determines there is a failure in the control logic foractuating SAV 50. Rather, the secondary startup procedure assumes thatpneumatic power is provided to starter motor 38, regardless of theability of FADEC system 52 to control SAV 50, due to SAV 50 being openedmanually.

In one embodiment, FADEC system 52 receives feedback on a temperaturewithin turbine engine 10, and executes the secondary startup procedureonly if the temperature is less than a predetermined threshold (shown atbox 110). FADEC system 52 executes the secondary startup procedure onlyif the temperature is less than the predetermined threshold such thatthermal rotor bow has either decreased, or has been entirely mitigatedprior to engine startup. Alternatively, any feedback may be used todetermine when the secondary startup procedure may be executed (i.e.,when turbine engine 10 can be motored at full power without causing apotentially harmful vibratory response). For example, alternativefeedback includes an amount of time that has passed since shutdown ofturbine engine 10.

Referring to FIG. 7, a crew logic diagram for starting turbine engine 10with SAV 50 that can only be fully opened is shown. As shown, thecockpit crew determines if FADEC system 52 has control over SAV 50(shown at box 112). If not, the cockpit crew determines if the enginetemperature is less than a predetermined threshold (shown at box 114).The lack of logic in the secondary startup procedure for actuating SAV50 results in uncontrolled motoring of turbine engine 10 (shown in FIG.1), and turbine engine 10 is allowed to cool (shown at box 116) suchthat the uncontrolled motoring does not result in forming a potentiallyharmful vibratory response in turbine engine 10. Alternatively, otheroperating parameters of turbine engine 10, such as time since engineshutdown, are, used to determine when uncontrolled motoring of turbineengine 10 may be implemented. Once turbine engine 10 has cooled, SAV 50is fully opened (shown at box 118) and a command to start the engine isexecuted (shown at box 120).

Referring to FIG. 8, and as described above, SAV 50 is capable of beingopened manually into an intermediate position between the closedposition and the open position to facilitate mitigating thermal rotorbow. Opening SAV 50 into the intermediate position (shown at box 122)causes turbine engine 10 to reach a motoring speed that is high enoughto mitigate the thermal rotor bow but low enough to avoid creating avibratory response and potentially damaging turbine engine 10. As such,in the manual mode of actuation, the thermal rotor bow is mitigatedmanually prior to fully opening SAV 50 (shown at box 118). Turbineengine 10 then receives a command from the cockpit (shown at box 120),for example, which causes turbine engine 10 to start. As such, turbineengine 10 can be started without waiting for turbine engine 10 to fullycool.

Any suitable indication that thermal rotor bow has been mitigated may beprovided to personnel within the cockpit that enables the systems andmethods to function as described herein. For example, in one embodiment,SAV 50 is manually opened and held in the intermediate position for apredetermined amount of time, and the cockpit command to start turbineengine 10 is provided after the predetermined amount of time has run.Alternatively, FADEC system 52 monitors the motoring progress of turbineengine 10 (e.g., motoring speed and time, engine internal temperature,and vibration levels), and provides an indication to the cockpit thatthe rotor bow has been mitigated. This logic may be embodied in FADECsystem 52, an aircraft, or any other suitable computer system.

In embodiments where FADEC system 52 does not have control over SAV 50,the motoring speed of turbine engine 10 can be controlled using any ofthe control arrangements described above. For example, uncontrolledmotoring of turbine engine 10 can result in motoring speeds greater thanthe resonant rotational speed. As such, FADEC system 52 controlsactuation of modulating valve 54, actuation of any combination of theadditional valves, such as discharge or bypass valves 55, in startersystem 42, actuation of variable stator vanes 56, or the power output ofalternative actuating power sources for starter motor 38 for reducingthe motoring speed of turbine engine 10.

Moreover, FADEC system 52 monitors at least one operating parameter ofturbine engine 10 to determine how much and when the motoring speed ofturbine engine 10 can be increased. More specifically, FADEC system 52monitors an operating parameter of turbine engine 10, such as thevibratory response of turbine engine 10, as turbine engine 10 is rotatedat the initial motoring speed, and increases the motoring speed ofturbine engine 10 when the vibratory response decreases. For example,the motoring speed of turbine engine 10 is increased by controllingactuation of modulating valve 54, actuation of any combination of theadditional valves in starter system 42, actuation of variable statorvanes 56, or the power output of alternative actuating power sources forstarter motor 38. As such, the motoring time of turbine engine 10 isreduced.

A method of operating a turbine engine is also described herein. Themethod includes monitoring at least one operating parameter of theturbine engine, determining a preset motoring time for the turbineengine based on a value of the at least one operating parameter, andactuating a starter motor of the turbine engine such that the turbineengine is rotated at a motoring speed, the starter motor actuated for atleast the preset motoring time.

Determining a preset motoring time includes selecting the presetmotoring time from a plurality of preset motoring times, each presetmotoring time of the plurality of preset motoring times corresponding toa different value of the at least one operating parameter. Determining apreset motoring time further includes determining the preset motoringtime based at least partially on a temperature within the turbineengine. Determining a preset motoring time further includes monitoring atemperature of an ambient environment outside the turbine engine,determining a temperature difference between the temperature within theturbine engine and the temperature of the ambient environment, anddetermining the preset motoring time based on a value of the temperaturedifference.

Monitoring at least one operating parameter of the turbine engineincludes monitoring a vibratory response of the turbine engine as theturbine engine is rotated at the motoring speed. The method furtherincludes adding additional time to the preset motoring time based on avalue of the vibratory response. The method further includes monitoringthe at least one operating parameter for an adjustment in a value ofvibratory response as the turbine engine is rotated at the motoringspeed, and increasing the motoring speed of the turbine engine when thevibratory response decreases.

The method further includes shutting down the starter motor such thatthe starter motor is actuated for an amount of time less than or equalto a predetermined duration. The method further includes actuating aplurality of variable stator vanes of the turbine engine such that theplurality of variable stator vanes are at least partially open tocontrol the motoring speed of the turbine engine. The method furtherincludes controlling a power output of a power source configured toactuate the starter motor of the turbine engine, wherein the poweroutput is selected such that a predetermined power output is provided tothe starter motor, and adjusting a position of a valve coupled betweenthe power source and the starter motor, the position of the valveadjusted to control the motoring speed of the turbine engine.

A starter system for use with a turbine engine is also described herein.The starter system includes a starter motor and a computing devicecoupled in communication with the starter motor. The computing device isconfigured to monitor at least one operating parameter of the turbineengine, determine a preset motoring time for the turbine engine based ona value of the at least one operating parameter, and actuate the startermotor such that the turbine engine is rotated at a motoring speed, thestarter motor actuated for at least the preset motoring time.

The starter system further includes at least one feedback sensor coupledin communication with the computing device. The at least one feedbacksensor is configured to monitor the at least one operating parameter ofthe turbine engine, and to transmit feedback to the computing device.The at least one feedback sensor is further configured to monitor atemperature within the turbine engine, and the computing device isfurther configured to determine the preset motoring time based at leastpartially on the temperature within the turbine engine. The at least onefeedback sensor is further configured to monitor a vibratory response ofthe turbine engine when rotated at the motoring speed, and the computingdevice is further configured to modify the preset motoring time based ona value of the vibratory response.

The computing device is further configured to shut down the startermotor such that the starter motor is actuated for an amount of time lessthan or equal to a predetermined duration.

A computer-readable medium having computer-executable instructionsembodied thereon for use in operating a turbine engine is also describedherein. When executed by at least one processor, the computer-executableinstructions cause the processor to monitor at least one operatingparameter of the turbine engine, determine a preset motoring time forthe turbine engine based on a value of the at least one operatingparameter, and actuate a starter motor of the turbine engine such thatthe turbine engine is rotated at a motoring speed, the starter motoractuated for at least the preset motoring time.

The computer-executable instructions further cause the processor toselect the preset motoring time from a plurality of preset motoringtimes, each preset motoring time of the plurality of preset motoringtimes corresponding to a different value of the at least one operatingparameter. The computer-executable instructions further cause theprocessor to determine the preset motoring time based at least partiallyon a temperature within the turbine engine. The computer-executableinstructions further cause the processor to monitor a vibratory responseof the turbine engine as the turbine engine is rotated at the motoringspeed, and modify the preset motoring time based on a value of thevibratory response. The computer-executable instructions further causethe processor to shut down the starter motor such that the starter motoris actuated for an amount of time less than or equal to a predeterminedduration.

A method of operating a turbine engine is also described herein. Themethod includes actuating a starter motor of the turbine engine suchthat the turbine engine is rotated at a motoring speed, monitoring atleast one operating parameter of the turbine engine, and determining amotoring time for the turbine engine based on a value of the at leastone operating parameter, the starter motor actuated for at least themotoring time.

Monitoring at least one operating parameter includes monitoring at leastone of a temperature within the turbine engine or a vibratory responseof the turbine engine. The method further includes adjusting themotoring time as a function of an adjustment in the value of the atleast one operating parameter as the turbine engine is rotated at themotoring speed. The method further includes determining a motoring speedfor the turbine engine based on the value of the at least one operatingparameter. The method further includes adjusting the motoring speed as afunction of an adjustment in the value of the at least one operatingparameter as the turbine engine is rotated at the motoring speed.

A method of operating a turbine engine is also described herein. Themethod includes providing a primary startup procedure and a secondarystartup procedure for the turbine engine and determining a mode ofactuation of a starter air valve from a closed position to an at leastpartially open position. The starter air valve is configured controlairflow channeled towards a starter motor of the turbine engine, whereinthe primary startup procedure includes an automatic mode of actuation ofthe starter air valve. The method also includes executing the secondarystartup procedure if the mode of actuation is not the automatic mode ofactuation.

A turbine engine is also described herein. The turbine engine includes astarter motor and a starter air valve configured to control airflowchanneled towards the starter motor. The starter air valve isselectively actuatable between a closed position and an open position.The turbine engine also includes a computing device coupled incommunication with the starter air valve. The computing device includesa primary startup procedure and a secondary startup procedure for theturbine engine stored thereon. The computing device is configured todetermine a mode of actuation of the starter air valve from the closedposition to an at least partially open position, wherein the primarystartup procedure includes an automatic mode of actuation of the starterair valve. The computing device is also configured to execute thesecondary startup procedure if the mode of actuation is not theautomatic mode of actuation.

A computer-readable medium having computer-executable instructionsembodied thereon for use in operating a turbine engine is also describedherein. The computer-executable instructions include a primary startupprocedure and a secondary startup procedure for the turbine engine,wherein, when executed by at least one processor, thecomputer-executable instructions cause the processor to determine a modeof actuation of a starter air valve of the turbine engine from a closedposition to an at least partially open position. The primary startupprocedure includes an automatic mode of actuation of the starter airvalve. The computer-executable instructions also cause the processor toexecute the secondary startup procedure if the mode of actuation is notthe automatic mode of actuation.

An exemplary technical effect of the system and methods described hereinincludes at least one of: (a) actively controlling the rotational speedof a turbine engine during startup with existing internal enginecontrols; (b) facilitate controlling the rotational speed of the turbineengine below a resonant rotational speed; (c) reducing contact-relatedwear between rotating and stationary components of the turbine enginecaused as a result of thermal rotor bow; (d) enabling a starter systemto be operated normally (i.e., at full torque) while still controllingthe motoring speed of the turbine engine during startup; (e) reducingstartup time for the turbine engine; (f) enabling manual startup of aturbine engine; and (g) bypassing a primary startup procedure for asecondary startup procedure that enables the manual startup.

Exemplary embodiments of a turbine engine and related components aredescribed above in detail. The system is not limited to the specificembodiments described herein, but rather, components of systems and/orsteps of the methods may be utilized independently and separately fromother components and/or steps described herein. For example, theconfiguration of components described herein may also be used incombination with other processes, and is not limited to practice withonly turbine engines and related methods as described herein. Rather,the exemplary embodiment can be implemented and utilized in connectionwith many applications where improving or preserving turbine engineperformance is desired.

Although specific features of various embodiments of the presentdisclosure may be shown in some drawings and not in others, this is forconvenience only. In accordance with the principles of embodiments ofthe present disclosure, any feature of a drawing may be referencedand/or claimed in combination with any feature of any other drawing.

Some embodiments involve the use of one or more electronic or computingdevices. Such devices typically include a processor or controller, suchas a general purpose central processing unit (CPU), a graphicsprocessing unit (GPU), a microcontroller, a reduced instruction setcomputer (RISC) processor, an application specific integrated circuit(ASIC), a programmable logic circuit (PLC), and/or any other circuit orprocessor capable of executing the functions described herein. Themethods described herein may be encoded as executable instructionsembodied in a computer readable medium, including, without limitation, astorage device and/or a memory device. Such instructions, when executedby a processor, cause the processor to perform at least a portion of themethods described herein. The above examples are exemplary only, andthus are not intended to limit any way the definition and/or meaning ofthe term processor.

This written description uses examples to disclose the embodiments ofthe present disclosure, including the best mode, and also to enable anyperson skilled in the art to practice embodiments of the presentdisclosure, including making and using any devices or systems andperforming any incorporated methods. The patentable scope of theembodiments described herein is defined by the claims, and may includeother examples that occur to those skilled in the art. Such otherexamples are intended to be within the scope of the claims if they havestructural elements that do not differ from the literal language of theclaims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.

What is claimed is:
 1. A method of mitigating thermal rotor bow in aturbine engine, said method comprising: operating the turbine engineunder normal operating conditions; shutting down the turbine engine,wherein thermal rotor bow occurs; monitoring at least one parameterindicative of the rotor bow of the turbine engine; in response to the atleast one parameter, using a controller to: actuate a starter motor ofthe turbine engine to cause a rotor assembly of the turbine engine torotate; and actuate a plurality of variable stator vanes of the turbineengine such that the plurality of variable stator vanes are at leastpartially open to increase a counter-rotational torque on the rotorassembly of the turbine engine in opposition to the starter motor,wherein the starter motor and plurality of variable stator vanescooperate to control a motoring speed of the rotor assembly such thatthermal rotor bow in the turbine engine is mitigated.
 2. The method inaccordance with claim 1, wherein actuating a plurality of variablestator vanes comprises adjusting a position of the plurality of variablestator vanes such that the motoring speed of the turbine engine isgreater than a predetermined motoring speed.
 3. The method in accordancewith claim 1, wherein actuating a plurality of variable stator vanescomprises: monitoring a vibratory response of the turbine engine as theturbine engine is rotated at the motoring speed; and adjusting theposition of the plurality of variable stator vanes such that thevibratory response is less than a predetermined threshold.
 4. The methodin accordance with claim 1, wherein actuating a plurality of variablestator vanes comprises adjusting a position of the plurality of variablestator vanes such that the motoring speed of the turbine engine ismaximized relative to a resonant rotational speed of the turbine engine.5. The method in accordance with claim 4, wherein adjusting the positionof the plurality of stator vanes comprises: monitoring a vibratoryresponse of the turbine engine as the turbine engine is rotated at themotoring speed; and adjusting the position of the plurality of variablestator vanes such that the motoring speed of the turbine engineincreases when the vibratory response decreases.
 6. The method inaccordance with claim 4, wherein adjusting the position of the pluralityof stator vanes comprises: monitoring a temperature within the turbineengine as the turbine engine is rotated at the motoring speed; andadjusting the position of the plurality of variable stator vanes suchthat the motoring speed of the turbine engine increases when thetemperature decreases.
 7. The method in accordance with claim 1 furthercomprising: actuating the starter motor at a power output for rotatingthe turbine engine at a motoring speed greater than a resonantrotational speed of the turbine engine; and adjusting a position of theplurality of variable stator vanes into an at least partially openposition to reduce the motoring speed of the turbine engine.
 8. Themethod in accordance with claim 1 further comprising shutting down thestarter motor such that the starter motor is actuated for an amount oftime less than or equal to a predetermined duration.
 9. A turbine enginecomprising: a starter motor; a compressor assembly comprising aplurality of variable stator vanes; and a computing device monitoring atleast one parameter of the turbine engine and coupled in communicationwith said starter motor and said plurality of variable stator vanes tomitigate thermal rotor bow during startup of the turbine engine, saidcomputing device configured to: actuate said starter motor of theturbine engine such that a motoring speed of the turbine engineincreases; monitor a temperature within the turbine engine as theturbine engine is rotated at the motoring speed; actuate said pluralityof variable stator vanes such that said plurality of variable statorvanes are at least partially open to control the motoring speed of theturbine engine; and adjust a position of the plurality of variablestator vanes such that the motoring speed of the turbine engineincreases when the temperature decreases, wherein thermal rotor bow inthe turbine engine is mitigated.
 10. The turbine engine in accordancewith claim 9, wherein said computing device is further configured toadjust a position of the plurality of variable stator vanes such thatthe motoring speed of the turbine engine is greater than a predeterminedmotoring speed.
 11. The turbine engine in accordance with claim 9,wherein said computing device is further configured to: monitor avibratory response of the turbine engine as the turbine engine isrotated at the motoring speed; and adjust the position of said pluralityof variable stator vanes such that the vibratory response is less than apredetermined threshold.
 12. The turbine engine in accordance with claim9, wherein said computing device is further configured to adjust aposition of said plurality of variable stator vanes such that themotoring speed of the turbine engine is maximized relative to a resonantrotational speed of the turbine engine.
 13. The turbine engine inaccordance with claim 12, wherein said computing device is furtherconfigured to: monitor a vibratory response of the turbine engine as theturbine engine is rotated at the motoring speed; and adjust the positionof said plurality of variable stator vanes such that the motoring speedof the turbine engine increases when the vibratory response decreases.14. The turbine engine in accordance with claim 9, wherein saidcomputing device is further configured to: actuate said starter motor ata power output for rotating the turbine engine at a motoring speedgreater than a resonant rotational speed of the turbine engine; andadjust a position of said plurality of variable stator vanes into an atleast partially open position to reduce the motoring speed of theturbine engine.
 15. The turbine engine in accordance with claim 9,wherein said computing device is further configured to shut down saidstarter motor such that said starter motor is actuated for an amount oftime less than or equal to a predetermined duration.
 16. Anon-transitory computer-readable medium having computer-executableinstructions embodied thereon for use in operating a turbine engine,wherein, when executed by at least one processor, thecomputer-executable instructions cause the processor to: monitor atleast one parameter related to thermal rotor bow of the turbine engineand in response to the at least one parameter, the computer-executableinstructions cause the processor to: actuate a starter motor of theturbine engine during startup such that a motoring speed of the turbineengine increases; monitoring a temperature within the turbine engine asthe turbine engine is rotated at the motoring speed; and actuate aplurality of variable stator vanes of the turbine engine such that theplurality of variable stator vanes are at least partially open tocontrol the motoring speed of the turbine engine and such that themotoring speed of the turbine engine increases when the temperaturedecreases, wherein the actuating of the starter motor and plurality ofvariable stator vanes mitigates thermal rotor bow in turbine engineduring startup.
 17. The non-transitory computer-readable media inaccordance with claim 16, wherein the computer-executable instructionsfurther cause the processor to: monitor a vibratory response of theturbine engine as the turbine engine is rotated at the motoring speed;and adjust the position of the plurality of variable stator vanes suchthat the vibratory response is less than a predetermined threshold. 18.The non-transitory computer-readable media in accordance with claim 16,wherein the computer-executable instructions further cause the processorto adjust a position of the plurality of variable stator vanes such thatthe motoring speed of the turbine engine is maximized relative to aresonant rotational speed of the turbine engine.
 19. The non-transitorycomputer-readable media in accordance with claim 18, wherein thecomputer-executable instructions further cause the processor to: monitora vibratory response of the turbine engine as the turbine engine isrotated at the motoring speed; and adjust the position of the pluralityof variable stator vanes such that the motoring speed of the turbineengine increases when the vibratory response decreases.
 20. Thenon-transitory computer-readable media in accordance with claim 16,wherein the computer-executable instructions further cause the processorto: actuate the starter motor at a power output for rotating the turbineengine at a motoring speed greater than a resonant rotational speed ofthe turbine engine; and adjust a position of the plurality of variablestator vanes into an at least partially open position to reduce themotoring speed of the turbine engine.
 21. The non-transitorycomputer-readable media in accordance with claim 16, wherein thecomputer-executable instructions further cause the processor to shutdown the starter motor such that the starter motor is actuated for anamount of time less than or equal to a predetermined duration.